1. Field of the Invention
The present disclosure generally relates to operating liquid crystal devices and displays. More particularly, the disclosure generally relates to systems and methods for reducing acoustical noise associated with the operation of liquid crystal displays and especially associated with the operation of three dimensional liquid crystal displays using modified driving waveforms.
2. Description of the Relevant Art
Some of the advantages of a liquid crystal display (LCD) include lighter weight, lower power consumption, and less radiation contamination. LCD monitors have been widely applied to various portable information products, such as notebooks, mobile phones, PDAs, etc. Typically in an LCD monitor, incident light produces different polarization or refraction effects when the alignment of liquid crystal molecules is altered. The transmission of the incident light is affected by the liquid crystal molecules, and thus a magnitude of the light emitted from the liquid crystal molecules varies. The LCD monitor utilizes the characteristics of the liquid crystal molecules to control the corresponding light transmittance and produces images according to different magnitudes of red, blue, and green light.
A schematic image of a nematic liquid crystalline phase 100 is shown in FIG. 1. The liquid crystal materials have no positional long-range ordering of their molecules' centers of mass, as in crystals. However, the liquid crystal materials possess long-range orientational ordering of their molecules along a main axis direction (in the simplest case of so-called nematic liquid crystal), effectively allowing the molecules to be aligned along one preferred direction, called the director of the liquid crystal, {right arrow over (n)} (see FIG. 1).
Liquid crystal molecules either possess a permanent dipole moment, or acquire the induced dipole moment when placed in an electric field. In both cases, in the electric field a liquid crystal molecule 200 is characterized by some dipole moment, μ. This dipole may be aligned along the molecule's symmetry axis (such materials are said to have the positive dielectric anisotropy) or perpendicular to it (the negative dielectric anisotropy). The separation of charge in a molecule leads to its rotation in the electric field until it is aligned parallel or perpendicular to the applied field, depending on a sign of the material's dielectric anisotropy. FIG. 2 depicts such re-orientation of a liquid crystal molecule with the positive dielectric anisotropy.
As all of the molecules in the liquid crystalline phase are subject to the re-orientation under the effect of the electric field at the same time, it is possible to control the symmetry axis of the phase (the director) and usually the optical axis of the liquid crystalline sample.
FIG. 3 illustrates the configuration of liquid crystal molecules 300 within a conventional twisted nematic liquid crystal based polarization rotator. The nematic liquid crystal is chosen to have a positive dielectric anisotropy. The left hand side of the figure illustrates the voltage OFF, 90 degree rotation state. The right hand side of the figure illustrates the voltage ON, 0 degree rotation state.
Depending on the type of the liquid crystal cell and the relative orientations of the liquid crystal cell's optical axis and the polarizers' transmission axis, the polarization rotator can operate in either Normal White (NW) or Normal Black (NB) mode. These modes are governed by the optical transmission in the zero or low-voltage state, i.e. the Normal White mode corresponds to the maximum optical transmission in the zero or low-voltage state, and the minimum transmission in the high-voltage state; it is the opposite for the Normal Black mode.
The twisted nematic polarization rotator usually operates in the Normal White mode. In this case the higher applied voltage improves the contrast ratio of the Normal White mode due to the decrease of the residual retardation of a liquid crystal cell.
Other type of polarization rotators such as electrically controlled birefringence (ECB) mode can operate both in Normal White and Normal Black modes. Using additional optical elements in the 3D system (such as two orthogonal polarizers), the same polarization rotator can operate in the both modes alternately in each every frame.
FIGS. 4A-C illustrate the standard “square wave” AC driving waveform (FIG. 4C) that is used in the simple driving schemes of an LCD, as well as the resulting optical response (FIG. 4A). It produces the fastest switching between the states of a liquid crystal cell.
In 3D systems based on the use of an on-screen polarization rotator, higher applied voltage frequently leads to better system performance, such as increased contrast and faster switching time.
In practice, in some cases higher driving voltage may lead to the unwanted acoustical noise effect (“buzzing”). This effect gets more noticeable for the large surface area and small cell gap liquid crystal cells, such as the aforesaid polarization rotator.
Therefore a system and/or method which results in lowering to a minimum or eliminating the level of the acoustical noise during the polarization rotator operation would be highly desirable.